Astonished astronomers said Wednesday they had found rings around an asteroid, the smallest object known to have this feature and only the fifth after Jupiter, Saturn, Uranus and Neptune.
The twin rings around a rock called Chariklo were spotted in June last year as it passed in front of a star. As expected, the star seemed to vanish for a few seconds as Chariklo blocked its light — a phenomenon known as occultation. But the mini-eclipse turned out to be much more than the astronomers were expecting. Two narrow, dense rings — a feature believed to be limited to the four giant planets of our Solar System were blocking the light of the star. In a new paper in Nature, the team of scientists not only reconstructed the shape and size of Chariklo itself but also the shape, width and orientation of its twin halos.
These were seven and three km (4.3 and 1.8 miles) wide respectively, separated by a nine-km gap. Like Saturn’s rings, Chariklo’s may be composed of water ice.
Chariklo is a lumpy 250-km-wide rock discovered in 1997 and named after a water nymph in Greek mythology. It orbits the Sun between Saturn and Uranus, more than a billion kilometres from Earth. It is a Centaur, a category of celestial bodies that share the characteristics of comets, which are made of ice and dust and form tails when they pass near the Sun, and asteroids which are made of metallic rock, have shorter orbits and tend to cluster in groups. Centaurs have unstable orbits that cross those of the giant planets and live for a few million years.
Origin of Chariklo’s rings
The origin of Chariklo’s rings are a mystery for now, but may be the result of a debris-releasing collision with another body.
A ring system detected around the Centaur (10199) Chariklo Braga-Ribas, F. et al. Nature http://dx.doi.org/10.1038/nature13155